This invention relates to a film depositing apparatus and a method for depositing a film on the surface of a base.
Recently, in the field of electronic copying machines, the use of an amorphous silicon photoconductor for a photosensitive layer has been proposed. A photosensitive body with an amorphous silicon photoconductor as a photosensitive layer (hereinafter referred to simply as an .alpha.-Si photosensitive body) is superior to those materials, such as .alpha.-Se, CdS, ZnO, O.P.C., etc. (which are presently used as photosensitive layers for electronic copying machines) with regard to properties such as thermal resistance, hardness, durability and non-polluting effect.
The .alpha.-Si photosensitive body is manufactured by, for example, the glow discharge method as follows. As shown in FIGS. 1 and 2, a drum-shaped base 12 is rotatably housed in a casing 10. A vacuum is previously formed inside the casing 10 by a diffusion pump and a rotary pump (not shown). The base 12 is grounded, and is rotated about its own axis by a drive mechanism (not shown). When a valve 18 is opened, SiH.sub.4 (silane) gas or a mixture of SiH.sub.4 and B.sub.2 H.sub.6 or of SiH.sub.4 and PH.sub.3, as required, is led into the casing 10. At the same time, an exhaust system is shifted from the position where it is connected to the diffusion pump and the rotary pump (not shown) to the position where it is connected to a mechanical booster pump 14 and a rotary pump 16. The introduced gas is blown against the surface of the base 12 through a number of gas nozzles 22 of a gas inlet pipe 20. The base 12 is heated by a heater 24. The gas inlet pipe 20 serves also as the cathode of a radio-frequency power source 26. After the internal pressure of the casing 10 is adjusted to a predetermined level by controlling a valve (not shown) included in the exhaust system, radio-frequency power from the power source 26 is applied between the cathode 20 and the base 12. Since the base 12 is grounded, it functions as an anode compared with the cathode 20. As a result, glow discharge is caused between the gas inlet pipe 20 as the cathode and the base 12 as the anode to activate (or ionize) the SiH.sub.4 gas. Thus, with the passage of time, .alpha.-Si develops over the surface of the base 12. Consequently during the deposition of the .alpha.-Si film, the radical of SiH.sub.4 gas, which hs not taken part in the film deposition, is sucked out from the casing 10 by the mechanical booster pump 14 and the rotary pump 16, a photosensitive layer of .alpha.-Si is deposited on the surface of the base 12 to a given thickness. Thereafter, the radical of the SiH.sub.4 gas is safely discharged to the outside air through a combustion tower and a scrubber (not shown) in succession. Then, the casing 10 is opened, and the .alpha.-Si photosensitive body is taken out therefrom. Thus, the manufacture of a single .alpha.-Si photosensitive body is completed.
In the manufacture of the .alpha.-Si photosensitive body in this manner, however, the film depositing speed is extremely low, and preprocessing for evacuating the casing 10 and post-processing for discharging the residual radical of SiH.sub.4 in the casing 10 are substantially prolonged which lowers productivity. Thus, the manufacturing cost of the .alpha.-Si photosensitive body obtained is very high.
To eliminate these drawbacks, there is conventionally proposed a method in which a plurality of drum-shaped bases 12 are arranged axially, as shown in FIG. 3, so that .alpha.-Si films may be simultaneously deposited on the multitude of bases 12. According to this method, however, the number of bases 12 set in the casing 10 are limited because of the height limit of the casing 10, and the casing 10 makes inserting and removing the bases 12 inconvenient. With this film depositing method, moreover, vacuum pumps (not shown) are required to be mounted at the lower portion of the casing 10. Accordingly, the gas density inside the casing 10 is not uniform, so that the photosensitive layers of .alpha.-Si deposited on the bases 12 are subject to variation in thickness. This is a fatal drawback.